Bell Labs, the research arm of Alcatel-Lucent, has demonstrated the use of two copper telephone lines to achieve broadband download speeds of up to 300Mbps.

The technique could offer another way of rolling out faster broadband — complementing current cable and fibre-optic rollouts — and could extend the life of copper-based broadband networks in the face of competition from other technologies, Alcatel-Lucent said in an announcement on Wednesday.

"At these speeds, service providers will be able to maximise the ability of the existing copper infrastructure — widely deployed around the world — to satisfy demand for bandwidth-intense residential triple-play and business services for years to come," the company said in its announcement.

Alcatel-Lucent used DSL phantom mode — an analogue telephony technique first developed in 1886 — to add a virtual third channel on top of the two normally transmitted over a twisted-pair copper telephone line.

The technique adds to the bandwidth the line can carry, but also introduces more noise into the signal. A second technique — called vectoring — was used to cancel out this noise. A third technique — called bonding — was used to treat two telephone lines as though they were a single cable, further extending bandwidth.

In a laboratory demonstration, the resulting connection achieved downstream transmission speeds of 300Mbps over distances of up to 400 metres, or up to 100Mbps at up to 1 kilometre, Alcatel-Lucent said.

By contrast, BT currently offers download speeds of up to 20Mbps on its standard ADSL broadband services. The telco is currently in the process of rolling out broadband packages with speeds of up to 40Mbps or 100Mbps, but these involve running fibre either to the user's local telephone exchange or to the premises. BT has said it is planning to have four million homes connected to fibre-based broadband by the end of this year, with 10 million connected by early 2012.

Virgin Media offers cable-based broadband services at speeds going up to 10Mbps, 20Mbps and 50Mbps, and is rolling out 100Mbps broadband this year.

"What makes DSL phantom mode such an important breakthrough is that it combines cutting-edge technology with an attractive business model that will open up entirely new commercial opportunities for service providers, enabling them in particular to offer the latest broadband IP-based services using existing network infrastructure," said Gee Rittenhouse, head of research at Bell Labs, in a statement.

Alcatel-Lucent's technique requires the user to have two telephone lines already installed on the premises, as well as a modem specifically geared to use two lines. The company said it is currently carrying out further research into how service providers could deploy the technology.